How to handle equality constraints in the mutation operation of evolutionary algorithms?
If X is your 6D vector and m(X) is the mutated version of X, then you can renormalise the mutant back to unity by dividing by the sum of X, i.e. X' = m(X)/sum(X).
However, I encourage you figure out how to mutate a vector while keeping the length of the vector at 1. One way to do this would be to randomly rotate your vector in 6D space. The length should stay the same, and you don't need to renormalise it afterwards.